Range sensor and range image sensor

ABSTRACT

The range image sensor is a range image sensor which is provided on a semiconductor substrate with an imaging region composed of a plurality of two-dimensionally arranged units (pixel P), thereby obtaining a range image on the basis of charge quantities Q L , Q R  output from the units. One of the units is provided with a charge generating region (region outside a transfer electrode  5 ) where charges are generated in response to incident light, at least two semiconductor regions  3  which are arranged spatially apart to collect charges from the charge generating region, and a transfer electrode  5  which is installed at each periphery of the semiconductor region  3 , given a charge transfer signal different in phase, and surrounding the semiconductor region  3.

This is a continuation application of copending application Ser. No.12/992,422, having a §371 date of Feb. 23, 2011, which is a nationalstage filing based on PCT International Application No.PCT/JP2009/058572, filed on May 1, 2009. The copending application Ser.No. 12/992,422 is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates to a range sensor and a range image sensorloaded on product monitors in a production line of a factory as well ason vehicles and others.

BACKGROUND ART

A conventional range finder has been described, for example, in PatentLiterature 1. In the present range image sensor, all four sides of aphoto sensitive region into which light is made incident are surroundedby four transfer gate electrodes, transfer voltages different in phaseare applied to these transfer gate electrodes, and charges generated ata photo sensitive region will flow sequentially into four chargeaccumulating regions located outside the transfer gate electrodes. Inthe range image sensor, on the basis of charge quantities distributedinto the accumulating regions, a distance to an object is calculated.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Translation of International    Application (Kohyo) No. 2000-517427

SUMMARY OF INVENTION Technical Problem

However, since a range image sensor having a conventional range sensoris constituted so as to surround the periphery of a subtle-lightincident region with four triangular transfer gate electrodes, it ispoor in aperture ratio and also unable to collect charges generated at aposition apart from the light incident region. Thus, the charges arecollected at a lower efficiency and uncollected charges are highlylikely to cause crosstalk. Further, an increase in pixels will require alonger transfer gate electrode. As described above, a conventional rangeimage sensor is unable to enhance an efficiency of collecting chargesand lower in signal level, thus failing in obtaining a range imageexcellent in S/N ratio.

The present invention has been made in view of the above problems, anobject of which is to provide a range sensor capable of obtainingdistance output excellent in S/N ratio and a range image sensor capableof obtaining a range image excellent in S/N ratio.

Solution to Problem

In order to solve the above-described problems, a range sensor of thepresent invention is provided with a charge generating region at whichcharges are generated in response to incident light, at least two chargecollecting regions which are arranged spatially apart from each other tocollect charges from the charge generating region and a transferelectrode which is installed at each periphery of the charge collectingregion, given a charge transfer signal different in phase, andsurrounding the charge collecting region. A range image sensor of thepresent invention is provided on a semiconductor substrate with animaging region composed of a plurality of two-dimensionally arrangedunits, wherein a range image is obtained on the basis of chargequantities output from the units. One of the units is composed of theabove-described range sensor.

A two-dimensional arrangement of a plurality of units results inlocation of a plurality of transfer electrodes at peripheries of thecharge generating regions. To put it the other way around, the chargegenerating regions are to locate also at peripheries of transferelectrodes. Since transfer electrodes surround the charge collectingregions, charge transfer signals are imparted to the transferelectrodes, thus making it possible to transfer charges from alldirections to the charge collecting regions. In other words,substantially all the peripheral regions of the transfer electrodes areallowed to function as a charge generating region, thereby remarkablyimproving an aperture ratio. Therefore, a signal level can be increasedto obtain a range image excellent in S/N ratio. With attention given toone range sensor, it is possible to transfer charges from all directionsoutside the transfer electrodes into the charge collecting regions, thusmaking it possible to collect a great quantity of charges. A distance ismeasured on the basis of the charges, by which distance output excellentin S/N ratio can be obtained.

It is also acceptable that at least two charge collecting regionssurrounded by transfer electrodes to which a charge transfer signal ofthe same phase is imparted are electrically connected. In this instance,charge quantities output from these charge collecting regions areaveraged, thus making it possible to compensate for a difference incharacteristics at each charge collecting region.

Further, it is preferable that a range image sensor of the presentinvention is additionally provided with potential adjusting meansinstalled at a charge generating region to make steep a potentialgradient from the charge generating region to a charge collectingregion. The potential adjusting means makes the potential gradientsteep, by which charges transferred from the charge generating region tothe charge collecting region will move at a high speed. In other words,high-speed imaging is made possible.

The above potential adjusting means is of a conductive type differentfrom the charge collecting region and can be constituted with asemiconductor region higher in impurity concentration than theperiphery. A difference in conductive type makes it possible to increasea potential gradient.

Further, the potential adjusting means is characterized in being anelectrode to which a predetermined potential is imparted. A potentialreverse to a potential by ionized donors or acceptors at the chargecollecting region is imparted to the above potential, by which it ispossible to increase a potential gradient.

Still further, a transfer electrode is preferably formed in an annularshape. Thereby, it is possible to reliably collect charges flowing intothe charge collecting region from all directions and also prevent theinflow. In addition, the transfer electrode can be formed in an annularshape having a gap. In this instance as well, it is possible to reliablycollect charges flowing into the charge collecting region from alldirections.

Advantageous Effects of Invention

According to a range sensor of the present invention, it is possible toobtain distance output higher in its charge collecting efficiency andexcellent in S/N ratio. According to a range image sensor using aplurality of the range sensors, it is possible to obtain a range imagehigher in its charge collecting efficiency and excellent in S/N ratio.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of an enlarged imaging region.

FIG. 2 is a cross sectional view taken along the arrow II-II of theimaging region.

FIG. 3 is a view showing potential distributions at the imaging region.

FIG. 4 is a timing chart of various signals.

FIG. 5 is a timing chart of various signals.

FIG. 6 is a partial cross sectional view of an imaging device with animaging chip given in FIG. 2 attached to a wiring substrate.

FIG. 7 is an overall cross sectional view of the imaging device.

FIG. 8 is a view showing an overall constitution of a range imagemeasuring device.

FIG. 9 is a circuit diagram inside a pixel.

FIG. 10 is a perspective view of an imaging region of the range imagesensor according to Embodiment 2.

FIG. 11 is a cross sectional view taken along the arrow XI-XI of theimaging region given in FIG. 10.

FIG. 12 is a perspective view of an imaging region of the range imagesensor according to Embodiment 3.

FIG. 13 is a cross sectional view taken along the arrow XIII-XIII of theimaging region given in FIG. 12.

FIG. 14 is a view for explaining pixel arrangements.

FIG. 15 is a view for explaining a connection at a received-chargecollecting region.

FIG. 16 is a view for explaining another constitution of a transferelectrode.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a description will be given of a range image sensor havinga range sensor according to embodiments of the present invention. It isnoted that the same elements will be given the same symbols and anoverlapping description will be omitted.

FIG. 1 is a perspective view of an imaging region of the range imagesensor according to Embodiment 1. FIG. 2 is a cross sectional view takenalong the arrow II-II of the imaging region.

On a p-type semiconductor substrate 1, there is grown a p-type epitaxiallayer 2 lower in concentration than the semiconductor substrate 1, andinside the epitaxial layer 2, an n-type semiconductor region (chargecollecting region) 3 higher in concentration is provided in a matrixform. It is noted that a substrate including the epitaxial layer 2 isalso to be a semiconductor substrate. The surface of the epitaxial layer2 is covered with an insulating layer 4 and on the insulating layer 4,there is installed a contact hole for exposing the surface of asemiconductor region 3. A conductor 7 for connecting the semiconductorregion 3 to the outside is passed through the contact hole.

On the insulating layer 4 at the periphery of the semiconductor region3, there is provided an annular transfer electrode (gate) 5. At a regionoutside the transfer electrode 5, a charge generating region is spreadout and at the center of the charge generating region inside pixels, apotential adjusting portion (potential adjusting means) 6 is installed.The potential adjusting portion 6 of the present embodiment is anelectrode arranged on the insulating layer 4. When an XYZ orthogonalcoordinate system is set, one pixel P is formed inside an XY plane togive a quadrangular shape, thereby constituting a range sensor. Thepotential adjusting portion 6 is located at the center of a pixel whichis a quadrangular shape, at a corner or at the middle point of eachside. Inside one pixel P, four transfer electrodes 5 are contained andlines connecting the centers of these are able to form a quadrangularshape. On the center of the diagonal lines, located is one potentialadjusting portion 6.

The semiconductor region 3 is to collect charges generated outsidetransfer electrodes 5, depending on light which is made incident. Atransfer electrode 5 in which a phase of a charge transfer signal to beapplied thereto is at 0 degrees is referred to as A, and that in whichthe phase is at 180 degrees is referred to as B. Regarding thesetransfer electrodes 5, those which are different in type are alternatelyarrayed along a direction of the X axis, and those different in type arealternately arrayed along a direction of the Y axis as well. In otherwords, when attention is given to one transfer electrode A, a transferelectrode B is adjacent in the direction of the X axis and in thedirection of the Y axis in the periphery thereof. When attention isgiven to one transfer electrode B, a transfer electrode A is adjacent inthe direction of the X axis and in the direction of the Y axis in theperiphery thereof. It is noted that when attention is given to a phaseof voltage applied to a transfer electrode, a description will be givenby referring to transfer electrodes A and B, and when an attention isgiven to a transfer electrode irrespective of the phase, a descriptionwill be given as transfer electrodes 5.

As light which is made incident into the center of one pixel P isconverted to a charge inside a semiconductor substrate, the thusgenerated charge travels to any direction of transfer electrodes 5 inaccordance with a potential gradient formed by a potential adjustingportion 6.

When a positive potential is imparted to a transfer electrode 5, a gateis opened by the transfer electrode 5, and a negative charge (electron)is drawn into a direction of the transfer electrode 5 and accumulatedinside a potential well formed by an n-type semiconductor region 3. Ann-type semiconductor contains a positively ionized donor to have apositive potential, thereby attracting electrons.

When a potential lower than the positive potential (ground potential) isimparted to a transfer electrode 5, a gate is closed by a transferelectrode 5 and charges generated at a semiconductor region 3 will notbe drawn into the semiconductor region 3.

It is noted that the semiconductor and the insulating layer 4 arerespectively made with Si and SiO₂, while the transfer electrode 5 andthe potential adjusting portion 6 are made with polysilicon. However,they may be made with different materials.

FIG. 3 is a view showing potential distributions at an imaging region.

FIG. 3( a) shows a potential diagram taken along a crosswise directionof the cross section given in FIG. 2 when a phase of a transferelectrode A is at 0 degrees, and FIG. 3( b) is a potential diagram takenalong a crosswise direction of the cross section given in FIG. 2 whenthe phase of the transfer electrode A is at 180 degrees. Further, FIG.3( c) is a potential diagram in a crosswise direction of the crosssection taken along the line C-C′ given in FIG. 1 in a state given inFIG. 3( a). It is noted that in FIG. 3, the downward direction indicatesa direction of a positive potential.

As shown in FIG. 3( a), when a phase of a transfer electrode A is at 0degrees, a positive potential is imparted to the transfer electrode A,while to a transfer electrode B, imparted is a reverse potential, inother words, a potential whose phase is at 180 degrees (groundpotential). In this instance, a negative charge e which is generated ata charge generating portion located between the transfer electrode A andthe transfer electrode B flows into a semiconductor region which isinside the transfer electrode A due to reduction in potential barrier ofa semiconductor immediately under the transfer electrode A. On the otherhand, there is no reduction in potential barrier of a semiconductorimmediately under the transfer electrode B, and no charge flows into thesemiconductor region 3 inside the transfer electrode B.

Further, as shown in FIG. 3( b), when a phase of a transfer electrode Bis at 0 degrees, a positive potential is imparted to the transferelectrode B, while to a transfer electrode A, imparted is a reversepotential, in other words, a potential whose phase is at 180 degrees(ground potential). In this instance, a negative charge e which isgenerated at a charge generating portion located between the transferelectrode A and the transfer electrode B flows into a semiconductorregion which is inside the transfer electrode B due to reduction inpotential barrier of a semiconductor immediately under the transferelectrode B. On the other hand, there is no reduction in potentialbarrier of a semiconductor immediately under the transfer electrode A,and no charge flows into the semiconductor region 3 inside the transferelectrode A.

Further, as shown in FIG. 3( c), normally, between a transfer electrodeA and a transfer electrode B, no potential adjusting portion 6 islocated. Inside a cross section which is not through the potentialadjusting portion 6, at a middle point between the transfer electrode Aand the transfer electrode B, there is observed no potential barrier asfound in FIG. 3( a) and FIG. 3( b). On the other hand, since the crosssections shown in FIG. 3( a) and FIG. 3( b) are through the potentialadjusting portion 6, energy is high at the middle point between thetransfer electrodes A and B and a potential gradient is steep to realizea high-speed charge transfer. It is noted that charges generated betweenthe transfer electrodes A and B given in FIG. 3( c) also flow into thesemiconductor region 3.

FIG. 4 is a timing chart of various signals.

There are shown a driving signal S_(D) of a light source to be describedlater, an intensity signal L_(P) of reflected light which returns backto an imaging region when the light source hits against an object, acharge transfer signal S_(L) applied to a transfer electrode A and acharge transfer signal S_(R) applied to a transfer electrode B. Sincethe charge transfer signal S_(L) is in synchronization with the drivingsignal S_(D), a phase of the intensity signal L_(P) of reflected lightwith respect to the charge transfer signal S_(L) is time-of-flight oflight, which indicates a distance between a sensor to an object. In thisinstance, upon application of the respective charge transfer signalsS_(L) and S_(R), a ratio of Q_(L) to Q_(R) which are quantities ofcharges collected at the semiconductor region 3 is used to calculate adistance d. In other words, when one pulse width of a driving signal isgiven as T_(P), there is obtained a formula, distanced=(c/2)×(T_(P)×Q_(R)/(Q_(L)+Q_(R))). It is noted that c denotes velocityof light.

FIG. 5 is a timing chart of various types of actual signals.

Within a term of one frame T_(F), when attention is given to one pixel,a driving signal S_(D) having a plurality of pulses is applied to alight source. In synchronization therewith, charge transfer signalsS_(L), S_(R) are applied to transfer electrodes A and B so as to bemutually reverse in phase. It is noted that prior to a distancemeasurement, a reset signal, reset, is applied to a semiconductor region3. Charges accumulated inside are discharged outside. In the presentembodiment, the reset signal, reset, is turned ON for a moment and thenturned OFF. Thereafter, a plurality of driving vibration pulses aresequentially applied and further, in synchronization therewith, chargesare sequentially transferred, and charges are cumulatively accumulatedinside the semiconductor region 3. Subsequently, before a next resetsignal, reset, is turned ON, charges accumulated inside thesemiconductor region 3 are read out.

FIG. 6 is a partial cross sectional view of an imaging device with animaging chip given in FIG. 2 attached to a wiring substrate.

This imaging device is that in which the imaging chip CP given in FIG. 2is inverted and stuck to a wiring substrate WB via a multilayer wiringsubstrate M1 and an adhesive agent FL. Inside the multilayer wiringsubstrate M1, there are provided through electrodes 7, 5E, 6E which areelectrically connected respectively to each of the semiconductor regions3, transfer electrodes 5 and potential adjusting portions 6. The throughelectrode 7 is connected via a bump electrode BP interposed between thewiring substrate WB and the multilayer wiring substrate M1 to a throughelectrode 8 of the wiring substrate WB. The through electrode 8 isexposed to the back of the wiring substrate WB. The through electrode 5Econnected to each transfer electrode 5 is connected via a wiring (notillustrated) to an internal wiring 50E of the wiring substrate WB. Onthe surface on a boundary face of an insulating substrate M2constituting the wiring substrate WB with the adhesive agent FL, alight-shielding layer 40 is formed, thereby preventing light which haspassed through the imaging chip CP from being made incident into thewiring substrate WB.

FIG. 7 is an overall cross sectional view of the imaging device.

This imaging device is a range image measuring device which is of backside illumination type. An enlarged view of a region surrounded by thebroken line G given in FIG. 7 corresponds to FIG. 6. The imaging chip CPis formed in such a manner that a central region CR is made thinner thana peripheral region PR, and the thinly formed region is given as animaging region, and reflected light IM from an object is made incident.Since this device is not provided with an electrode on a light incidenceside of a charge generating portion, it is possible to obtain distanceoutput and a range image which are high in S/N ratio.

FIG. 8 is a view showing an overall constitution of the range imagemeasuring device.

A distance, d, up to an object OJ is measured by a range image measuringdevice. As described above, to a light source 100 such as an LED, adriving signal S_(D) is applied, and an intensity signal L_(P) of areflected light image which has been reflected on the object OJ is madeincident into an imaging region IA of an imaging chip CP. From theimaging chip CP, at every pixel, charge quantities Q_(L), Q_(R)collected in synchronization with charge transfer signals S_(L), S_(R)are output. They are input into an arithmetic circuit ART insynchronization with a driving signal S_(D). At the arithmetic circuitART, as described above, the distance d is calculated at every pixel andcalculation results are transferred to a controlling section CONT. Thecontrolling section CONT controls a driving circuit DRV for driving alight source 100 and also outputs charge transfer signals S_(L), S_(R),thereby displaying the calculation results input from the arithmeticcircuit ART on a display DSP.

FIG. 9 is a circuit diagram inside a pixel.

If the potential adjusting portion 6 is given as a charge generatingregion, charges generated at this region are distributed inside thesemiconductor regions 3 on the right and left sides by alternatelyapplying voltages to transfer electrodes A, B. It is noted that thetransfer electrodes A, B constitute a gate electrode of eachelectrical-field effect transistor.

As described so far, the above-described range image sensor is a rangeimage sensor which is provided on a semiconductor substrate with animaging region composed of a plurality of two-dimensionally arrangedunits (pixel P), thereby obtaining a range image on the basis of chargequantities Q_(L), Q_(R) output from the units. One of the units isprovided with a charge generating region (region outside a transferelectrode 5) where charges are generated in response to incident light,at least two semiconductor regions (charge collecting regions) 3 whichare arranged spatially apart to collect charges from the chargegenerating region, and a transfer electrode 5 which is installed at eachperiphery of the semiconductor region 3, given a charge transfer signaldifferent in phase, and surrounding the semiconductor region 3.

Therefore, a two-dimensional arrangement of a plurality of pixels Presults in location of a plurality of transfer electrodes 5 atperipheries of charge generating regions. In another perspective, thecharge generating regions are to locate at peripheries of the transferelectrodes 5. Since the transfer electrodes 5 surround the semiconductorregion 3, charge transfer signals are imparted to the transferelectrodes 5, thereby making it possible to transfer charges from allthe directions to the semiconductor regions 3. In other words,substantially all peripheral regions of the transfer electrodes 5 areallowed to function as charge generating regions, thereby remarkablyimproving an aperture ratio. Therefore, a signal level can be increasedto obtain distance output excellent in S/N ratio and a range image asits aggregate information.

Further, the range image sensor of Embodiment 1 is provided with apotential adjusting portion 6 which is installed at a charge generatingregion to make steep a potential gradient from the charge generatingregion to a semiconductor region 3. The potential adjusting portion 6makes the potential gradient steep, by which charges are transferredfrom the charge generating region to the charge collecting region 3 at agreater moving speed. In other words, high-speed imaging is madepossible. It is noted that the potential adjusting portion 6 ofEmbodiment 1 is an electrode to which a predetermined potential isimparted. Preferably, in the present embodiment, to the electrodeimparted is a potential lower than the lowest value of a potentialimparted to a transfer electrode. Where a potential reverse to apotential resulting from a donor ionized at the charge collecting region(an acceptor where all conductive types are inverted) is imparted to theabove electrode, it is possible to increase the potential gradient.

Still further, a transfer electrode 5 is formed in an annular shape,thus making it possible to reliably collect charges flowing from all thedirections to a charge collecting region or prevent the inflow. Atransfer electrode 5 is formed in a circular annular shape but may beformed in an angular annular shape. As shown in FIG. 16, it may also beconstituted with a group of microelectrodes arranged apart along theannular shape. The transfer electrode 5 shown in FIG. 16 is that inwhich a plurality of partial transfer electrodes 51, 52, 53, 54, 55, 56,57, 58, 59 are arranged apart at equal intervals. Each of the partialtransfer electrodes 51 to 59 is formed in a circular arc shape, theinner side face of which runs along a circle indicated by the brokenline. As described above, the transfer electrode 5 is constitutedannularly so as to have a gap. However, in this instance, each of themicroelectrodes is to be electrically connected so that a potential canbe imparted simultaneously to all electrodes.

It is noted that in the above description, a region containing fourtransfer electrodes is given as one pixel. However, it may be a regioncontaining two transfer electrodes to which charge transfer signalsdifferent in phase are applied.

FIG. 10 is a perspective view of an imaging region of the range imagesensor according to Embodiment 2. FIG. 11 is a cross sectional viewtaken along the arrow XI-XI of the imaging region given in FIG. 10.

In Embodiment 1, as the potential adjusting portion 6, an electrode isused. The potential adjusting portion 6 of the present embodiment islocated within a plane which is the same as that of the potentialadjusting portion 6 in Embodiment 1 and a p-type semiconductor regionformed under an insulating layer 4. In this instance, the potentialadjusting portion 6 functions to increase a potential gradient as withEmbodiment 1.

The potential adjusting portion 6 of the present embodiment is ofconductive type different from the semiconductor region 3 andconstituted with semiconductor regions higher in impurity concentrationthan peripheries. Therefore, the potential adjusting portion 6 isdifferent in conductive type from the semiconductor region 3, thusmaking it possible to increase a potential gradient.

FIG. 12 is a perspective view of an imaging region of the range imagesensor according to Embodiment 3. FIG. 13 is a cross sectional viewtaken along the arrow XIII-XIII of the imaging region given in FIG. 12.

In the present embodiment, a transfer electrode 5 is constituted with anannular portion 5X and a radial portion 5Y extending outward radiallyfrom the annular portion 5X and not provided with a potential adjustingportion. The radial portion 5Y extends toward a site where the potentialadjusting portion has been located in the above-described embodimentsand is able to transfer charges generated around the site as well viathe radial portion 5Y into the semiconductor region 3.

FIG. 14 is a view for explaining pixel arrangements.

In Embodiments 1 to 3, as shown in FIG. 14( a), a description has beengiven that transfer electrodes A, B are arranged to give a quadrangularregion containing four transfer electrodes as one pixel P. It is alsoacceptable that a group containing eight transfer electrodes A, Bsurrounded by the single dotted and dashed line shown in FIG. 14( b) isgiven as one pixel P. In FIG. 14( b), two transfer electrodes A, Badjacent to each other at the center belong to both a group of fivetransfer electrodes A, B surrounded by the broken line and a group offive transfer electrodes A, B surrounded by the double dotted and dashedline. In this instance, as shown in FIG. 14( a), charges are collectedfrom a charge generating region that is almost twice the area comparedwith a case where a quadrangular region containing four transferelectrodes is given as one pixel. Therefore, such an effect is providedthat enhances distance accuracy.

FIG. 15 is a view for explaining a connection at a charge collectingregion.

In this constitution, within one pixel, at least two semiconductorregions 3 surrounded by transfer electrodes A to which a charge transfersignal of the same phase is imparted are electrically connected.Further, in this constitution, within one pixel, at least twosemiconductor regions 3 surrounded by transfer electrodes B to which acharge transfer signal of the same phase is imparted are electricallyconnected.

In order to connect semiconductor regions 3 surrounded by transferelectrodes A with each other, metal wires W1A, W1B, W1C are used. Themetal wire W1A connected to a first semiconductor region 3 surrounded bytransfer electrodes A is connected via a contact hole to the metal wireW1B, and the metal wire W1B is also connected via a contact hole to themetal wire W1C. The metal wire W1C is connected to a secondsemiconductor region 3.

Similarly, a metal wire W2A connected to a first semiconductor region 3surrounded by transfer electrodes B is connected via a contact hole to ametal wire W2B, and the metal wire W2B is also connected via a contacthole to a metal wire W2C. The metal wire W2C is connected to a secondsemiconductor region 3 surrounded by transfer electrodes B.

In this instance, charge quantities output from semiconductor regions 3of each group are averaged, thus making it possible to compensate for adifference in characteristics at each semiconductor region 3.

Further, as a charge collecting region, there is made an n-typesemiconductor region 3 higher in concentration in a p-type epitaxiallayer 2 which is grown on a p-type semiconductor substrate 1 and lowerin concentration than the p-type semiconductor substrate 1. However, ifa p-type layer higher in concentration than the p-type epitaxial layer 2is installed at the bottom of the n-type semiconductor region 3 higherin concentration (on a boundary face with the p-type epitaxial layer 2),it is preferably possible to suppress effects of an electric fieldresulting from application of voltage to the n-type semiconductor region3 higher in concentration. This is because, although there is such apossibility that application of voltage to the n-type semiconductorregion 3 higher in concentration may result in the spread of a depletedlayer between itself and the p-type epitaxial layer 2 and chargesgenerated by light may flow into the n-type semiconductor region 3higher in concentration due to the electric field inside the depletedlayer, irrespective of potentials of transfer electrodes, a p-type layerhigher in concentration than the p-type epitaxial layer 2 is installedunder the n-type semiconductor region 3 higher in concentration, thusmaking it possible to prevent substantial spread of the depleted layerin the p-type epitaxial layer 2. It is noted that the above-describedconductive types can be inverted all together.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a range sensor and a range imagesensor loaded on product monitors in a production line of a factory aswell as on vehicles and others.

REFERENCE SIGNS LIST

-   -   3: Semiconductor region (charge collecting region)    -   5, A, B: Transfer electrode    -   6: Potential adjusting portion

The invention claimed is:
 1. A range sensor comprising: a chargegenerating region at which charges are generated in response to incidentlight; a charge collecting region that collects the charges from thecharge generating region; a transfer electrode provided at a peripheryof the charge collecting region and completely surrounding the chargecollecting region, and a potential adjusting portion that increases apotential gradient from the charge generating region to the chargecollecting region.
 2. The range sensor according to claim 1, wherein thepotential adjusting portion comprises a semiconductor region including aconductivity type different from that of the charge collecting region,and having an impurity concentration higher than that of peripheral partof the semiconductor region.
 3. The range sensor according to claim 1,wherein the potential adjusting portion comprises an electrode to whicha predetermined potential is imparted.
 4. The range sensor according toclaim 1, wherein the number of the potential adjusting portion isplural, the plurality of the potential adjusting portions are arrangedat corners of a square, respectively, the diagonal lines of the squareintersect at a right angle, and the charge collecting region ispositioned at the intersection of the diagonal lines.
 5. The rangesensor according to claim 1, wherein the number of the charge collectingregion is plural, the potential adjusting portion is positioned betweenthe charge collecting regions, and the potential adjusting portion iscommonly used for the charge collecting regions.
 6. The range sensoraccording to claim 1, wherein a shape of the transfer electrode is anannular shape.
 7. A range image sensor comprising an imaging regioncomprised of a plurality of two-dimensionally arranged units on asemiconductor substrate, the imaging region obtaining range images basedon charges outputted from the units, wherein one of the units comprisesthe range sensor according to claim
 1. 8. A range image sensorcomprising an imaging region comprised of a plurality oftwo-dimensionally arranged units on a semiconductor substrate, theimaging region obtaining range images based on charges outputted fromthe units, wherein one of the units comprises the range sensor accordingto claim 1, and wherein the shape of the transfer electrode forms aring.
 9. A range image sensor comprising an imaging region comprised ofa plurality of two-dimensionally arranged units on a semiconductorsubstrate, the imaging region obtaining range images based on chargesoutputted from the units, wherein one of the units comprises the rangesensor according to claim 1, and wherein the transfer electrodetransfers charges generated out of a region of the transfer electrodeinto an inside region of the transfer electrode, the inside region isthe charge collecting region, and the charge collecting region isthoroughly surrounded by the transfer electrode.
 10. A range imagesensor comprising an imaging region comprised of a plurality oftwo-dimensionally arranged units on a semiconductor substrate, theimaging region obtaining range images based on charges outputted fromthe units, wherein one of the units comprises the range sensor accordingto claim 1, and wherein the transfer electrode transfers chargesgenerated out of a region of the transfer electrode into the chargecollecting regions from all directions.